The present invention relates to the removal of hydrogen sulfide from gas mixtures, particularly gas mixtures containing hydrocarbons such as, for example, natural gas.
The removal of H.sub.2 S from a gas stream is a problem that has long confronted and challenged workers in many diverse industries. One prime example is in the natural gas industry where the H.sub.2 S content of certain gas streams recovered from natural gas deposits in many areas of the world is too high for commercial acceptance. Over and above the environmental and safety hazards posed by the presence of H.sub.2 S in natural gas streams, the presence of such sulfur-containing compounds may result in the deposition of sulfur salts which can cause plugging and corrosion of transmission pipes, valves, regulators and the like. Even if the natural gas is flared as a waste stream, it is necessary that the H.sub.2 S either be completely removed or at least reduced to a level where the combustion products from the flaring do not introduce deleterious amounts of pollutants such as, for example, SO.sub.2, an ingredient of "acid rain. "
The "sweetening" or removal of H.sub.2 S from natural gas is only one example of where H.sub.2 S removal must be accomplished. In the manufactured gas industry or the coke-making industry, coal gas containing unacceptable amounts of H.sub.2 S is commonly produced by the destructive distillation of bituminus coal having high sulfur content. Another H.sub.2 S contamination problem is found in the manufacture of water gas or synthesis gas where it is not unusual to produce gas streams containing H.sub.2 S by passing steam over a bed of incandescent coke or coal containing a minor amount of sulfur. H.sub.2 S removal is also a frequently encountered problem in the petroleum refining industry because the principal raw material used, crude oil, typically contains minor amounts of sulfur--principally in the form of organic sulfur compounds. During the course of the many processes to which the crude oil or fractions thereof are subjected, one or more gas streams containing H.sub.2 S are quite commonly produced.
Regardless of the source of the gas stream, the problem of removing H.sub.2 S therefrom has been solved in numerous different ways which generally involve one or more of the following techniques: selective absorption with a wide variety of absorbents; absorption by suitable absorbent; and selective reaction with a reagent which produces an easily separable product. The details of these techniques are well known to those skilled in the art. The voluminous number of prior art processes, patents and publications dealing with the removal of H.sub.2 S from gas mixtures testifies to two facts: (1) the desirability, and in most cases, the necessity of removing the H.sub.2 S from the gas streams; and (2) that heretofore no completely desirable process has been found.
It is known that nitrous acid and nitrites, most commonly employed as oxidizing agents, can react in aqueous solutions with hydrogen sulfide to produce various oxidation products depending upon the pH. However, heretofore, it has not been proposed to remove hydrogen sulfide from gas mixtures, for example natural gas streams, by treating the gas mixture with an aqueous scrubbing or treating medium utilizing a water soluble nitrite.